Machine Design

Scanning for Ideas: Ballast-Free Ship Would Keep Lakes and Waterways Clean

Freighters carrying water for ballast have introduced over 150 nonnative creatures into the Great Lakes, including the zebra and quagga mussels.

Edited by Stephen J. Mraz

These species often cause havoc to other marine life and man-made structures. There are some moves to stop this, including a recently enacted regulation that says ships must flush their ballast tanks with saltwater before entering the St. Lawrence Seaway. There are also mandates for expensive UV or chemical-sterilization systems for ballast tanks. But researchers at the University of Michigan have come up with a new idea, one based on redesigning freighters and bulkcarrying ships.

Ships carry ballast to stay stable in the water when they are empty. The new ballastless ship would instead let fresh or saltwater flow through the ship from front to back. Water would travel slowly through a series of pipes (called trunks) that run below the waterline. This would keep the ship stable using local water. Ships would no longer haul ballast water, along with whatever is in it, from one port to another.

Tests on a scale model in a towing tank and a computer simulations indicate the design would also reduce the power needed to propel a ship by 7.3%. For a 650-ft freighter carrying 32,000 tons of cargo from the Great Lakes to Europe and back, that translates into a fuel savings of roughly $150,000.

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